Field of the Invention
The present invention relates to a vibration wave motor to be employed in, e.g., an optical device.
Description of the Related Art
Conventionally, ultrasonic motors are known as a technique in which a vibrator that vibrates periodically is pressed against and thereby brought into fictional contact with a friction member to move the vibrator and the friction member relative to each other. There is an example of making this type of ultrasonic motor into a linear ultrasonic motor for use in linear focusing driving of a taking lens. Japanese Patent Application Laid-Open No. 2014-183724 discloses a configuration in which a quadrangular prism-shaped friction member is arranged and a vibrator movably arranged on the friction member elliptically vibrates at an ultrasonic frequency, enabling linear driving. In this configuration, the vibrator is arranged on the friction member and a pressure mechanism for frictional contact of the vibrator is further laid on an upper portion of the friction member, resulting in increase in size of the ultrasonic motor.
In order to make an ultrasonic motor having such conventional configuration thinner, thinning of a friction member has been proposed; however, simple thinning of a friction member causes increase in number of vibration resonance points and thus frictional contact deterioration due to unwanted vibration, resulting in degradation in driving performance of the ultrasonic motor. Therefore, the friction member needs to have a certain degree of dimension in a thickness direction, which hinders thinning of the ultrasonic motor.